LED lamps have the advantages of long service life, small size and environmental protection, etc., so their applications are increasing more and more. However, the light emitting surface of the LED lamps generally is small due to the LED packaging holder and the substrate which blocks the light, and the LED lamps presents the status of lighting in half of circumference where the angle of the light distribution is less than 180 degree.
To achieve a similar light distribution with incandescent lamp of which the light distribution is more than 180 degree, some LED bulb lamps adopt COB (Chip On Board) integrated light sources and is configured with light distribution lens, and some adopt SMD (Surface Mount Technology) light sources arranged on the substrate in an encircling manner. Nevertheless, the light shape curves of these LED bulb lamps are not smooth and have higher local jitter, which result in a situation in which the brightness transits unevenly.
In addition, the traditional LED bulb lamp generally has a glass lamp housing which is fragile and the glass fragments can hurt users easily, further, after being broken, the exposed and charged part in the lamp body, such as the light source, solder joints on the substrate or the wires on the lamp substrate etc., will lead to an accident of electric shock easily and result in the risk of personal safety.
Recently, LED light bulbs each of which has an LED filament for emitting light are commercially available. The LED filament includes a substrate plate and several LEDs on the substrate plate. The effect of illumination of the LED light bulb has room for improvement. A traditional light bulb having a tungsten filament can create the effect of even illumination light because of the nature of the tungsten filament; however, the LED filament is hard to generate the effect of even illumination light. There are some reasons as to why the LED filament is hard to create the effect of even illumination light. One reason is that the substrate plate blocks light rays emitted from the LEDs. Another reason is that the LED generates point source of light, which leads to the concentration of light rays. In contrast, to reach the effect of even illumination light requires even distribution of light rays.
In addition, a traditional light bulb having a tungsten filament with elaborate curvatures and varied shapes could present an aesthetical appearance, especially when the traditional light bulb is lighting. The LED filament of the LED light bulb is difficult to be bent to form curvature because the substrate plate causes less flexibility. Further, electrodes on the LED filament and wires connecting the electrodes with the LEDs may be broken or disconnected when the LED filament is bent due to stress concentration.